Exelixis Inc.'s MEK-inhibitor cobimetinib, given in combination with Roche AG's Zelboraf (vemurafenib), significantly improved overall survival (OS) vs. Zelboraf alone for previously untreated patients with unresectable locally advanced or metastatic melanoma carrying a BRAF V600 mutation, according to new top-line results reported by Exelixis partner Genentech, a unit of Roche.